BACS Velcro fasteners on PP battery cases

Fixing the sticking problems with batteries using polypropylene
and flame-retardant plastics

Bonding PP and ABS surfaces: What you need to pay attention to

Polypropylene (PP) and acrylonitrile butadiene styrene (ABS) are two of the most widely used industrial plastics. They are found in a variety of applications, from the automotive industry to household appliances to many manufacturers' battery products. Although PP and ABS have many similarities, in addition to the cheaper price of PP, there are also some important chemical differences that cause adhesion problems between BACS and the battery housing.

Surface energy differences between PP and ABS

One of the most significant differences is the surface energy. Surface energy is a measure of how well a material is wetted by another material. The higher the surface energy, the better the wetting - and thus the adhesive properties.
PP has a low surface energy while ABS has a high surface energy. Surface energy plays a key role in bonding because it influences the wetting of the substrate by the adhesive. Wetting is the process by which the adhesive spreads across the surface of the substrate. Good wetting is important to ensure a strong and lasting bond. This means that adhesives designed for ABS will not adhere well to PP surfaces, and vice versa.
To achieve a permanent bond between PP and ABS surfaces, it is important to use an adhesive specifically designed for use with the respective materials.

Which adhesive pads are delivered as standard with BACS?

The BACS module housing is made of flame-retardant ABS plastic, the same material as the housings of most batteries on the market. The Velcro tape for positioning the BACS module uses an adhesive that is “safe” and does not pose a risk to the surface to which it is stuck (no solvent, which could potentially remove the plasticizer from plastics and risk damaging the battery case). The adhesive and Velcro combination that BACS uses as standard is the 3M Type 3550 with “DUAL LOCK” and has been used millions of times on all types of battery cases worldwide for more than 15 years.

Since most batteries on the market are made of ABS plastic, an ABS adhesive pad is attached to the battery side as standard on every BACS module.

Customers for whom our ABS adhesive pads do not stick to the batteries often unknowingly use batteries whose housings are based on PP, which means that the 3M3550 pads cannot develop the usual adhesive strength on this material. The stiffness of the measuring cables (because they are halogen-free), which is often assumed to be the cause, is not the problem. It is not the stiffness of the halogen-free measuring cable that causes the modules to detach, but rather the plastic used in the battery housings!
The adhesive supplied with the BACS modules is developed for ABS plastics and therefore only sticks to PP polypropylene if it has a “smooth” surface. On smooth surfaces, the ABS adhesive also sticks perfectly to PP, as the adhesion forces of the smooth surface (e.g. Plexiglas as is common in wet rooms) can compensate for the deficit in the adhesive effect. This is not the case with the polypropylene plastics for VRLA batteries. Here the PP surface is “rough”, which means that the adhesive pads of the BACS modules, which initially seemed to stick well, later detach from the batteries as soon as the adhesion forces weaken due to the adhesive drying out due to the rough and therefore air-permeable surface of the battery, and the adhesive strength is then not sufficient.
Replacing it with new stickers specifically for PP - offered as a spare part under the order number "BACS_STRIP6" - solves the problem - permanently.

“BACS _STRIP6” for battery housing made of polypropylene (PP)

These alternative Velcro strips for use on PP materials are offered as a spare part (20 pieces per pack). These are already tailored for BACS modules and are compatible with the “Dual Lock”, the ABS side located on the BACS module. Now the battery adhesive side with the BACSSTRIP 6 offers significantly more adhesion of the adhesive on polypropylene surfaces. The original BACSSTRIP 5 remains on the ABS side of the BACS modules and ensures a perfect combination using the “Dual Lock”. The adhesive for BACS_STRIP 6 also comes from the manufacturer 3M and has the article name 3M3540.